**Hello ,**

**I have studied the boundary layer theory in my courses **

**But haven't learnt about the boundary layer separation **

**What is it exactly and how does it work ?**

**I have scrolled through the net but vague answers were all i could find **

**Thank You **

- 27 Views
- Last Post 03 June 2020
- Topic Is Solved

Mac123
posted this
26 May 2020

**Hello ,**

**I have studied the boundary layer theory in my courses **

**But haven't learnt about the boundary layer separation **

**What is it exactly and how does it work ?**

**I have scrolled through the net but vague answers were all i could find **

**Thank You **

Kremella
posted this
26 May 2020

Hello,

Boundary-layer separation occurs when the pressure-gradient in the streamwise direction becomes adverse and changes sign. For fluid to flow, a favorable pressure-gradient is generally required. However, this pressure-gradient sometimes changes sign near the wall and this causes local flow reversal. It is very well explained in the following textbook:

Viscous Fluid Flow by Frank White.

I hope this helps.

Best,

Karthik

Mac123
posted this
26 May 2020
- Last edited 26 May 2020

Thank You Mr Karthik

So as the fluid is essentially trying to overcome the viscous forces within the boundary layer

it moves towards a high pressure , which is the adverse pressure gradient ,

it stops the fluid flow(v=0) or causes it to reverse .

Right ?

Please correct me if i am wrong

Regards

Kremella
posted this
27 May 2020

When a fluid is flowing from A to B, it moves because of dP/dx > 0. It means the pressure at point A is greater than B and is referred to as a favorable pressure gradient. In the boundary layer, because of several reasons (such as changing curvature at the wall), this pressure gradient changes sign locally. Instead of dp/dx > 0, the local gradient is dP/dx < 0. This means that the downstream pressure is greater than upstream. This is generally an adverse pressure gradient and caused local flow reversal. When the velocity gradient becomes 0 at the wall, the flow lifts off and separates. I hope this helps understand.

Please mark the most appropriate answer as 'Is Solution' to help others.

Thanks.

Best,

Karthik

Mac123
posted this
02 June 2020

Hello,

I did not quite get you there .

So basically , when dP/dx<0 , velocity becomes zero and flow reversal happens ?

Kremella
posted this
02 June 2020

Yes. That is correct. When this happens near the wall, there is a local flow reversal.

Mac123
posted this
03 June 2020

So basically dP/dx<0 causes an increase in adverse pressure gradient.

Adverse pressure gradient relates to the downstream pressure .

So the point at which the velocity becomes zero , at the wall .

The flow reversal takes place ,

Right ?

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